1. Field of the Invention
The present invention relates to an afocal relay lens system for use with microscoper.
2. Description of the Prior Art
A microscope generally has such a construction as shown in FIG. 1 and is equipped on the side of the microscopist with an objective lens O which is not used for microscopy and which is a hindrant for observation. In order to correct this defect, it is necessary to construct the microscope as shown in FIG. 2. In order to design a microscope having such a construction as shown in FIG. 2, it is necessary to arrange a relay lens system between the objective lens and an eyepiece so that an image of an object formed by the objective lens is formed again at a predetermined position. Further, in a microscope system equipped with various accessories, a relay lens system is also required for changing the imaging position of the objective lens when the accessories are to be used for microscopy. There has conventionally been known a relay lens system comprising a concave lens group and a convex lens group for shifting the image position of the objective lens in microscopes as described above. When the imaging point of the microscope without using the relay lens system is represented by O.sub.1, the imaging point of the microscope using the relay lens system is designated by O.sub.2 ' and the image of O.sub.1 formed by the concave lens group L.sub.1 is denoted by O.sub.1 ' in a relay lens system consisting of the two concave and convex lens groups L.sub.1 and L.sub.2 as shown in FIG. 3, the image is shifted rearward for a distance of .epsilon..
When A.sub.1 O.sub.1 is represented by .alpha., A.sub.1 O.sub.1, is designated by .alpha.', A.sub.1 A.sub.2 is denoted by d, and focal lengths of the lens groups L.sub.1 and L.sub.2 are represented by f.sub.1 and f.sub.2 respectively in this figure, the following relations (1), (2) and (3) established by the imaging formula: ##EQU1## From these formulae (1) (2) and (3), f.sub.1 and f.sub.2 can be determined as follows: ##EQU2## Since the actual visual field of such a relay lens system is narrowed if it is of a magnifying type, or the image magnified by the objective lens is reduced if it is of a reducing type, both the types are undesirable. Further, a relay lens system designed for an fractional magnification level is undesirable since it results in an fractional magnification level of the entire microscope. Therefore, a relay lens system should preferably have a magnification level of 1x. When .beta. is set at 1 in the formulae (4) and (5) above, f.sub.1 and f.sub.2 are calculated by the following formulae (4') and (5') respectively: ##EQU3##
FIG. 4 illustrates shift of position Q of the exit pupil of the objective by a relay lens system consisting of the concave lens group L.sub.1 and convex lens group L.sub.2. In this figure, the reference symbol Q' represents an image of the entrance pupil Q formed by the lens group L.sub.1, the reference symbol Q" designates an image of Q' formed by the lens group L.sub.2, and the reference symbols Z.sub.1, Z.sub.1 ', Z.sub.2 and Z.sub.2 ' denote positions of Q, Q' and Q" as illustrated.
Examples of numerical data for relay lens systems consisting of such concave lens group L.sub.1 and convex lens group L.sub.2 will be described below: